Modular drilling system

ABSTRACT

A modular drilling system including a plurality of different size drill bits which can be interchangeably mounted on a common tapered male connecting portion of a drill rod assembly. The tapered male connecting portion may be formed directly onto a tapered drill rod of the assembly or may be formed on an adapter which is threaded onto a threaded drill rod of the assembly. Each bit includes a female connecting portion having a generally cylindrical tapered surface mating with a corresponding tapered surface of the male connecting portion and at least three planar sections adapted to provide positive engagement with corresponding planar sections of the male connecting portion.

This application claims foreign priority benefits from Australian Provisional Patent Application 2010903133 filed Jul. 14, 2010.

FIELD OF THE INVENTION

The present invention relates to a modular drilling system for use in mining and relates particularly, though not exclusively, to a modular drilling system used for drilling holes in a rock face using a percussion drill.

BACKGROUND

In underground and surface mining, for example gold mining, a decline provides access to gold-bearing zones or stopes at various levels below ground. The rock in a stope is blasted using suitable explosives to loosen the ore, which is then transported to the surface for processing. A systematic pattern of holes is drilled in the rock face and packed with explosive to break-up the rock into transportable pieces. Miners are responsible for drilling these holes with “jacklegs” or “jumbos.” A jackleg is a hydraulic drilling machine operated manually by a miner, whereas a jumbo is a wheeled vehicle with multiple drills mounted thereon for drilling multiple holes simultaneously.

Specially designed drill bits with tungsten carbide buttons are employed in jacklegs and jumbos to drill into the rock face using percussion drilling at the optimum rpm delivered by the machine. Conventional prior art drilling systems are of basically two types: those which use tapered bits, and those which use threaded bits. Both systems have advantages. The bits are generally robust and of high quality, and are available for a very wide range of hole sizes. However both prior art systems also have disadvantages. Threaded bits are more expensive than taper bits, and when the threaded connection fails the bit is lost. On the other hand taper bits do not remove easily and taper rod connections are easily damaged. Spinning of the taper bit at the taper connection can also occur under high rotational loads.

The present invention was developed with a view to providing a modular drilling system which is less susceptible to the above-noted disadvantages of the prior art and which retains the advantages of the prior art taper connections, and which may also serve to improve and enhance the presently used systems.

References to prior art in this specification are provided for illustrative purposes only and are not to be taken as an admission that such prior art is part of the common general knowledge.

SUMMARY

According to a one aspect of the present invention there is provided a drill bit for use with a male connecting portion of a drill rod assembly, the drill bit comprising:

a body extending in a longitudinal direction between a bit face at a forward end and a female connecting portion at a rear end;

the female connecting portion defining a socket comprising:

-   -   a generally cylindrical tapered surface adapted to form a mating         connection with a corresponding tapered surface of the male         connecting portion; and     -   at least three planar sections formed on the tapered surface at         evenly spaced apart positions in a circumferential direction         about the socket so as to be adapted to provide positive         engagement with corresponding planar sections of the male         connecting portion.

Preferably the drill bit is part of a modular system including a plurality of auxiliary bits, each having a bit face at a forward end and a female connecting portion at a rear end which is substantially identical to the female connecting portion of said drill bit while the bit faces of the plurality of auxiliary bits are different in size relative to one another.

In some instance the drill bits can be mounted directly on a drill rod of the drill rod assembly when the male connecting portion is formed directly on the drill rod so as to comprise:

a generally cylindrical tapered surface adapted to mate with the corresponding tapered surface of the female connecting portion; and

a planar section formed on the tapered surface in mating alignment with each of the planar sections of the female connecting portion.

Alternatively, the drill bits of the modular system may be provided in combination with an adapter having a rear end adapted to be supported on a drill rod of the drill rod assembly, for example by providing an internal thread adapted to engage in screw-threaded engagement with the male connecting portion of a threaded drill rod. In this instance, the male connecting portion is preferably defined on a forward end of the adapter so as to comprise a generally cylindrical tapered surface adapted to mate with the corresponding tapered surface of the female connecting portion, and a planar section formed on the tapered surface in mating alignment with each of the planar sections of the female connecting portion.

Preferably surface area of said at least three planar sections is at least 35% of a total surface area of the generally cylindrical tapered surface locating the planar sections thereon.

Preferably each planar section extends substantially a full length of the tapered female connecting portion.

Preferably the generally cylindrical tapered surface is oriented at a first inclination to a longitudinal axis of the drill bit and the planar sections are oriented at a second inclination to the longitudinal axis of the drill bit which is greater than the first inclination. In this instance a width of each planar section generally in the circumferential direction is reduced from the front end towards the rear end of the drill bit.

The first inclination is preferably less than 10 degrees and the second inclination is preferably within 3 degrees of the first inclination. More preferably, the first inclination is approximately 5 degrees and the second inclination is approximately 6 degrees such that the second inclination differs by approximately one degree from the first inclination.

When the male connecting portion includes an outer end face at a forward end and the socket of the female connection portion comprises an internal end face, preferably the planar sections are oriented relative to the internal end face such that:

-   -   the internal end face is adapted to be spaced from the outer end         face of the male connecting portion when the planar sections of         the female connecting portion initially abut the planar sections         of the male connecting portion; and     -   the internal end face is adapted to positively engage the outer         end face of the male connecting portion when the drill bit is         subjected to percussive drilling forces from the drill rod         assembly.

Particularly in the instance when the male connecting portion is formed on the adapter, the male connecting portion may be further integrally connected to a body portion (typically the body of the adapter) which is preferably formed at the rear end of the male connecting portion and has a greater diameter than the male connecting portion so as to define an annular shoulder about a rear end of the male connecting portion. The shoulder advantageously resists the plastic deformation of the bit from ever reaching a critical point to resist catastrophic failure of the drill bit a commonly occurs by the breaking of the drill bit skirt in the prior art.

When the male connecting portion includes the annular shoulder about the rear end thereof and the socket of the female connection portion comprises annular end face at the rear end, preferably the planar sections are oriented relative to the annular end face such that:

-   -   the annular end face is adapted to be spaced from the annular         shoulder of the male connecting portion when the planar sections         of the female connecting portion initially abut the planar         sections of the male connecting portion; and     -   the annular end face is adapted to positively engage the annular         shoulder of the male connecting portion when the drill bit is         subjected to percussive drilling forces from the drill rod         assembly.

When using an adapter, the body of the drill bit can be formed of a material having a greater hardness than the adapter. Alternatively, the adapter can be made of a harder wearing material or material which is heat treated differently to ensure that the adapter lasts many times longer than the bit.

The drill bit preferably comprises a type in which the bit face includes a plurality of protrusions radially and circumferentially spaced from one another and being formed of a material having a greater hardness than the body of the drill bit.

According to a second aspect of the present invention there is provided a modular drilling system for use with a male connecting portion of a drill rod assembly, the system comprising:

a plurality of drill bits, each having a body extending in a longitudinal direction between a bit face at a forward end and a female connecting portion at a rear end;

the female connecting portion of each drill bit defining a socket comprising:

-   -   a generally cylindrical tapered surface adapted to form a mating         connection with a corresponding tapered surface of the male         connecting portion; and     -   at least three planar sections formed on the tapered surface at         evenly spaced apart positions in a circumferential direction         about the socket so as to be adapted to provide positive         engagement with corresponding planar sections of the male         connecting portion;

the female connecting portions of the drill bits being substantially identical to one another; and

the bit faces of the plurality of auxiliary bits being different in size relative to one another.

According to a further aspect of the present invention there is provided a modular drilling system for use with a male connecting portion of a drill rod assembly, the system comprising:

an adapter having a rear end comprising a female connecting portion formed with an internal thread so as to be adapted to engage in screw-threaded engagement with a male portion of a threaded drill rod of the drill rod assembly and a forward end defining a common male connecting portion comprising:

-   -   a generally cylindrical tapered surface; and     -   at least three planar sections formed on the tapered surface at         evenly spaced apart positions in a circumferential direction;         and

a plurality of drill bits, each having a body extending in a longitudinal direction between a bit face at a forward end and a female connecting portion at a rear end, the bit faces of the plurality of auxiliary bits being different in size relative to one another, and the female connecting portion of each drill bit defining a socket comprising:

-   -   a generally cylindrical tapered surface adapted to form a mating         connection with the corresponding tapered surface of the common         male connecting portion of the adapter; and     -   a planar section formed on the tapered surface of the female         connecting portion in alignment with each of the planar sections         of the male connecting portion of the adapter so as to be         adapted to provide positive engagement of the planar sections of         the drill bit with the corresponding planar sections of the male         connecting portion of the adapter.

The use of 3 planar surfaces, particularly when representing approximately 35% of the total load transfer area, provides for optimal rotational axis load torque to strengthen the male and female connection and allows for enough conical surface area for optimal load transfer of the percussive forces. By arranging the planar surfaces to be bigger on the top of the cone and smaller down the shaft it allows for more material on the bit internally thus making the bit stronger and less prone to taper failures. The increase in material is achieved by having the planar surface at an angle that is different from the conical tapered surface.

The 3 planar surfaces also tie in with the frequency of the percussion hammer and allow for the hole being drilled to have perfect geometry (round). If less than 3 planar sections are used, the frequency of the percussion hammer allows the bit load to misdirect and cause non circular holes to be drilled (oval or triangular).

The planar angles and conical surface angles are also arranged to allow enough movement when drilling starts to ensure additional surfaces to meet for enhanced power transmission and still continue to allow the bind to be strong enough to hold the bit on the tapered connection. Otherwise the bit will shoot off the male taper end if the angles are too steep and the surfaces meet during drilling.

The bits are thus held onto the tapered drill rod by hammering so that a tight friction fit is the only thing retaining the bit on the tapered drill rod. By optimizing the angles used, the friction fit gets stronger. Friction and plastic deformation keeps the bind. When the deformation is at its limits however, critical a failure occurs. The modular taper connection as described herein however has the advantage of stopping the plastic deformation when the faces meet during drilling.

The adapter reduces material use and allows for different materials to be used so that one can put harder metal and harder working parts on an adaptor which can be made of cheaper material. One can use a number of different sized bits on the adaptor because the better power transmission allows larger bits to be used. The modular profile and load transfer properties of the drill bit and corresponding male connecting portion of a drill rod or adapter in a drill rod assembly extends the bit size beyond the current head size range of bits and has additional load transfer faces only after the bit has started drilling. The advantages in the market place are:

i) that a single adapter, threaded onto one of the standard drill rods can be safely used with several different diameter bits and with a reduced risk of failure of the drill rod on which the bit is mounted, thus reducing overall inventory;

ii) the bits are cheaper because they use less materials than the competing products in some drilling applications, particularly in the larger diameters because they do not include an integral part that includes the threaded section;

iii) in smaller diameter bits that might previously have been on a tapered steel fitting, higher power levels can now be applied because of the unique shape of the contact power transfer faces in the modular fittings; and

iv) the bits can be easily replaced when worn and the adapter section does not get thrown out until worn. The life of the adapter is typically in the order or three times the life of the drill bit being used.

Although tapered bits are used in limited low cost applications, the users now have the option of getting all the benefits from a threaded rod system where the modular bit is removable. The cost of the improved product will be the same as the standard tapered bit system in the market. When using threaded button bits users will have the same function with more benefits and greater savings.

Throughout the specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. Likewise the word “preferably” or variations such as “preferred”, will be understood to imply that a stated integer or group of integers is desirable but not essential to the working of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature of the invention will be better understood from the following detailed description of a specific embodiment of a modular drilling system, given by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a side elevation of a preferred embodiment of a drill bit for a modular drilling system in accordance with the invention;

FIG. 2 is a rear plan view of the drill bit of FIG. 1;

FIG. 3 is a section view of the drill bit of FIG. 1 connected to the end of a drill rod;

FIG. 4 is front perspective view of the drill bit of FIG. 1;

FIG. 5 is a rear perspective view of the drill bit of FIG. 1;

FIG. 6 is a front perspective view of a drill rod adaptor for a modular drilling system in accordance with the invention;

FIG. 7 is a front plan view of the drill rod adaptor of FIG. 6;

FIG. 8 is a section view showing drill bit of FIG. 1 and the drill rod adaptor of FIG. 7 connected to a threaded drill rod; and,

FIG. 9 is a front perspective view of the drill bit of FIG. 1 being received on the front of the drill rod adaptor of FIG. 6.

DETAILED DESCRIPTION

Referring to the accompanying figures there is illustrated a modular drilling system comprising a plurality of drill bits 10 which are arranged to be interchangeably supported on a tapered male connecting portion of a drill rod assembly 5.

According to a first embodiment as shown in FIGS. 1 through 5, the drill rod assembly comprises a drill rod 18 directly locating the tapered male connecting portion 22 thereon.

Alternatively according to a second embodiment as shown in FIGS. 6 through 9, the drill rod assembly comprises a threaded drill rod 38 having a threaded male connecting portion at the forward end thereof for receiving an adapter 30 thereon in threaded connection. The tapered male connecting portion 34 in this instance is located on the forward end of the adapter 30.

The drill bit 10 and the tapered male connecting portions 22 or 34 remain substantially identical between the two embodiments. Accordingly the common features will now be described.

The drill bit 10 comprises a generally cylindrical body extending in a longitudinal direction between a forward end and an opposing rear end. The forward end defines a bit face locating a plurality of carbide buttons 20 protruding therefrom such that the buttons are spaced apart in a circumferential direction and in a radial direction relative to a longitudinal axis of the cylindrical body of the drill bit. The plurality of drill bits 10 within the modular system typically have different size bit faces for drilling different size holes in the rock.

The rear end of the drill bit includes a tapered female connecting portion 12 in the form of a socket extending inwardly into the body from an annular shoulder 45 at the rear end about the socket opening to an internal end face 46 defining a terminal end of the socket bore. The socket has an internal tapered surface which is generally cylindrical in shape and which is tapered so as to be generally conical and so as to be reduced in diameter from the greatest diameter at the rear end of the bit to the smallest diameter adjacent the internal end face of the socket. The tapered surface in the illustrated embodiment is oriented at a first inclination relative to the longitudinal axis of the bit which is approximately 5 degrees.

A set of three planar sections 14 are formed in the tapered surface at evenly spaced positions in the circumferential direction about the longitudinal axis of the bit. Each planar section comprises a planar surface spanning a full length of the socket between the annular shoulder 45 at the rear of the bit and the internal end face 46. The planar sections are oriented at a second inclination relative to the longitudinal axis of the bit which is approximately 6 degrees in the illustrated embodiment so as to be greater in inclination than the tapered surface by approximately 1 degree.

The resulting width of the planar sections in a generally circumferential or tangential direction relative to the longitudinal axis of the bit is arranged to be greatest at an inner end adjacent to the internal end face 46. The width becomes narrower from the front end towards the rear end of the bit. The resulting surface area of the three planar sections 14 together relative to the overall surface area of the planar sections with the remaining portions of the generally cylindrical tapered surface of the socket is approximately 35% in the illustrated embodiment. The planar sections 14 of the bit are thus adapted to provide positive engagement with a corresponding tapered surface of the male connecting portion 22 or 34.

The plurality of drill bits 10 forming a set of bits within the modular drilling system have female tapered connecting portions which are identical in size and configuration to one another for being commonly received on a common configuration of tapered male connecting portion 22 or 34.

In each instance, the tapered male connecting portion 22 or 34 comprises a generally cylindrical tapered surface 50 which is reduced in diameter from a rear end to a forward end terminating at an outer end face 44 which is arranged for insertion into the female connecting portion 12 of the bits 10. The tapered surface 50 is similar in shape and orientation as the corresponding tapered surface of the female connecting portion 12.

The tapered surface 50 also has three planar sections 14 or 42 formed thereon which are evenly spaced in the circumferential direction, span a full length of the tapered surface 50 in the longitudinal direction, and are oriented similarly to the planar sections 14 of the bits 10 for mating connection therewith.

The internal end face 46 of the bit socket and the planar sections 14 are oriented relative to one another such that the internal end face is adapted to be spaced from the outer end face 44 of the male connecting portion when the planar sections of the female connecting portion initially abut the planar sections of the male connecting portion during assembly. When the drill bit is subjected to percussive drilling forces from the drill rod assembly the internal end face is adapted to positively engage the outer end face of the male connecting portion.

Turning now more particularly to the embodiment of FIGS. 6 through 9, the adapter 30 has a body portion 32 which is generally cylindrical about a longitudinal axis of the body extending between the rear end locating a female connecting portion 36 therein and a forward end locating the male connecting portion 34. The female connecting portion 36 is an internally threaded socket which is arranged to receive the male threaded connecting portion at the forward end of an externally threaded drill rod 38.

The body portion of the adapter is integrally connected to and formed at the rear end of male connecting portion such that the male connecting portion 34 protrudes forwardly outward beyond an end of a main cylindrical portion of the adapter body 32. The body portion 32 has a greater diameter than a greatest diameter of the tapered surface 50 of the male connecting portion such that an annular shoulder 43 is defined about the rear end of the male connecting portion 34 at the forward end of the cylindrical body. The annular shoulder 43 is substantially perpendicular to the longitudinal direction similarly to the annular shoulder 45 at the rear end of the bit.

In this instance, the annular end face at the rear end of the bit, the annular shoulder of the adapter body and the planar sections of the tapered connection can be oriented relative to one another such that the annular end face is adapted to be spaced from the annular shoulder of the male connecting portion when the planar sections of the female connecting portion initially abut the planar sections of the male connecting portion. When the drill bit is subjected to percussive drilling forces from the drill rod assembly however, the annular end face is adapted to positively engage the annular shoulder of the male connecting portion to increase drilling force in the longitudinal direction.

The resulting modular drilling system is well suited to providing long drilling life relative to the overall cost of the drilling components. Typically the buttons 20 are made of a carbide material having a greater hardness than the body of the drill bit while the drill bit is made of material which can still be harder and more durable than the material of the adapter to reduce the cost of the threaded connection to a threaded drill rod without compromising the strength and life of the drill bit.

As described above, according to a preferred embodiment, the drill bit 10 for the modular drilling system in accordance with the invention, as illustrated in FIGS. 1 to 5, comprises the tapered female connecting portion 12 having at least one planar section 14 to provide positive engagement with the male connecting portion 16 on a drill rod 18 at a taper connection (see FIG. 3). The female connecting portion 12 is typically in the form of a conical socket or bore within which the male connecting portion of a drill rod is received in a friction fit. The modular drilling system typically has a plurality of drill bits 10 of various sizes. As noted above, each drill bit 10 typically has a series of hardened protrusions on its front face, for example, carbide buttons 20, for rock-breaking ability of the drill bit.

Preferably the plurality of planar sections 14 are arranged at uniformly spaced intervals about the circumference of the tapered female connecting portion 12 such that the three planar sections 14 are oriented about the circumference of the female connecting portion 12 at 120° intervals. Each planar section 14 extends substantially the full length of the tapered female connecting portion 12.

The modular drilling system preferably further comprises a drill rod 18 having a tapered male connecting portion 22 for connecting the drill rod 18 to a drill bit 10 (see FIG. 3). The male connecting portion 22 is typically in the form of a conical boss which is adapted to be received in the female connecting portion 12 of a drill bit 10. The male connecting portion 22 has three planar section 24 adapted to provide positive engagement with a planar section 14 on the female connecting portion 12 of a modular drill bit.

Preferably the male connecting portion 22 on the drill rod 18 has a corresponding number of planar sections 24 arranged at uniformly spaced intervals about its circumference. In use, the positive engagement of the matching planar sections at the taper connection ensures that a cyclical load is more uniformly distributed at the taper connection. The planar sections can be at a different or same angle than the conical surface.

When the first connection is made between the modular drill bit 10 and modular drill rod 22 there will be a unseen gap in-between the faces on the inside modular drill bit female connection 46 and the top of the modular drill rod connection 44. When the drilling process starts the gap will disappear and there will be an additional face where load will transfer through. These faces meet due to the angle of the conical surfaces and the angles of planar sections on the conical surfaces and load that is applied.

Also as described above, the modular drilling system can further comprise a drill rod adaptor 30 comprising an elongate cylindrical body 32 having a tapered male connecting portion 34 at a front end thereof. The tapered male connecting portion 34 of the drill rod adaptor 30 is designed for positive engagement with the tapered female connecting portion 12 of a modular drill bit 10. The cylindrical body 32 of the drill rod adaptor 30 has a female connecting portion 36 at the rear end for engagement with an end of a conventional drill rod 38 (see FIG. 8). The male connecting portion 34 has at least one planar section 42 adapted to provide positive engagement with a planar section 14 on the female connecting portion 12 of a modular drill bit.

When the first connection is made between the modular drill bit 10 and modular drill rod adaptor 34 there will be a gap in-between the faces on the bottom modular drill bit 45 and the top of the modular drill rod adaptor shoulder 43. When the drilling process starts the gap will disappear and there will be an additional face where load will transfer through. These faces meet due to the angle of the conical surfaces and the angles of planar sections on the conical surfaces and load that is applied.

Typically the conventional drill rod is a threaded drill rod 38 and the female connection portion 36 of the drill rod adaptor 30 is formed with the internal thread adapted to engage in screw-threaded engagement with the male connecting portion 40 of a threaded drill rod 38. The provision of the drill rod adaptor 30 means that the modular drill bits 10 can be used with a conventional drill rod, simply by connecting a drill rod adaptor 30 to the end of the drill rod 38. The drill bit 10 can be readily swapped over with another modular drill bit 10 of a different size or less worn, without the problems associated with the prior art threaded drill bits.

As described herein, for optimal rotational axis load torque, 3 planar surfaces are provided of approx 35% of total load transfer area, to strengthen the male and female connection and allow for enough conical surface area for load transfer. There could be more planar sections; however, the optimum balance is 3. When 4 or more planar sections is applied, the male connection becomes the weak point as material has been removed from the male connection and added to the bit connection which could make the connection fail. One would also have to make the connections longer and bigger to accommodate the stresses applied which will add more cost to the component. Alternatively, if the connection is made any shorter it would fail for the simple reason that there is not enough surface area and material to allow a proper bind.

There is a 1 degree offset at the base of the male taper. This allows for the planar section to be slightly bigger at the front than the base. This feature gives the bit connection more material at the deepest end of the socket. It gives it additional strength to handle the percussive forces applied by the hammer and gives the taper the additional strength where most needed as this is where failures occur the most in the existing art.

Typically the power transfer is so efficient the drill bit head size can be increased to take addition load. Also the increase in material is achieved by having the planar surface at an angle that is different from the conical tapered surface.

It has been found through testing that optimal angles are 5 degrees of inclination for the conical taper and 6 degrees of inclination for the planar surfaces as measured relative to a longitudinal axis of the bit connection. These angles give the correct bind or holding power and enough rotational torque.

The planar angles and conical surface angles are very important as they allow enough movement when drilling starts to ensure additional surfaces to meet for enhanced power transmission and still allows the bind to be strong enough to hold the bit on the tapered connection. This a very simple principle that if the angle is too steep on the taper surfaces it does not give the correct bind that will hold the bit on the front of the taper connection, when the percussive forces go through the component.

The other main reason for having 3 planar surfaces is that it ties in with the frequency of the percussion hammer and allows for the hole being drilled to have perfect round geometry. If less than 3 planar sections are used, the frequency of the percussion hammer allows the bit load to misdirect and cause non circular holes to be drilled (oval or triangular). This arises because the drill bit has a number of carbide bullets that are spaced radially and circumferentially at certain intervals around the circumference and face of the bit. If only 1 or 2 planar sections are provided in the bit there would be very high stress load on the planar sections causing the bit to react on those forces.

The annular shoulder is also unique to the modular design as it allows the bit to move down the taper when drilling starts to meet the face of the modular adaptor and then deliver additional power to the bit.

Rope (R—Range) and square threads (FI and T—Range) are the industry standard for connection to threaded drill rods and are used all over the world in mining applications. In the current adaptor 30 of the modular drilling system there will typically only be one size adaptor even if the bit head size changes for a range of drill bits. If the client wants the rods machined for the modular taper after the threads are worn this can be done and the modular drill bit can fit straight on the rods with no adapter.

Now that a preferred embodiment of the modular drilling system has been described in detail, it will be apparent that the described embodiment provides a number of advantages over the prior art, including the following:

(i) The modular drill bits have a much lower cost of production than the prior art threaded bits.

(ii) The positive engagement of the modular bits means that the head size of the modular bit can be increased due to cyclical forces being distributed more uniformly at the taper connection and connecting faces.

(iii) The modular bits can be adapted to any current prior art drilling system without modification.

(iv) The modular drill bit can be changed for a larger or smaller head sizes and still use the same modular adaptor.

(v) The modular system can be used in DTH (Down the hole hammer) applications as well with similar advantages.

(vi) When the modular adaptor's threaded connection is worn the modular drill head can be taken off and used again with another modular adaptor.

(vii) Users have the option of resharpening modular drill bits or not.

It will be readily apparent to persons skilled in the relevant arts that various modifications and improvements may be made to the foregoing embodiments, in addition to those already described, without departing from the basic inventive concepts of the present invention. For example, the drill rod adaptor can be provided with a different kind of female connecting portion at the rear end for connection to other types of conventional drill rod. Therefore, it will be appreciated that the scope of the invention is not limited to the specific embodiments described. 

1. A drill bit for use with a male connecting portion of a drill rod assembly, the drill bit comprising: a body extending in a longitudinal direction between a bit face at a forward end and a female connecting portion at a rear end; the female connecting portion defining a socket comprising: a generally cylindrical tapered surface adapted to form a mating connection with a corresponding tapered surface of the male connecting portion; and at least three planar sections formed on the tapered surface at evenly spaced apart positions in a circumferential direction about the socket so as to be adapted to provide positive engagement with corresponding planar sections of the male connecting portion.
 2. The drill bit according to claim 1 in combination with a plurality of auxiliary bits, each having a bit face at a forward end and a female connecting portion at a rear end which is substantially identical to the female connecting portion of said drill bit, the bit faces of the plurality of auxiliary bits being different in size relative to one another.
 3. The drill bit according to claim 1 in combination with a drill rod of the drill rod assembly, the male connecting portion being defined on drill rod so as to comprise: a generally cylindrical tapered surface adapted to mate with the corresponding tapered surface of the female connecting portion; and a planar section formed on the tapered surface in mating alignment with each of the planar sections of the female connecting portion.
 4. The drill bit according to claim 1 in combination with an adapter having a rear end adapted to be supported on a drill rod of the drill rod assembly, the male connecting portion being defined on a forward end of the adapter so as to comprise: a generally cylindrical tapered surface adapted to mate with the corresponding tapered surface of the female connecting portion; and a planar section formed on the tapered surface in mating alignment with each of the planar sections of the female connecting portion.
 5. The drill bit according to claim 4 wherein the rear end of the adapter comprises a female connecting portion formed with an internal thread adapted to engage in screw-threaded engagement with the male connecting portion of a threaded drill rod.
 6. The drill bit according to claim 1 wherein a surface area of said at least three planar sections is at least 35% of a total surface area of the generally cylindrical tapered surface locating the planar sections thereon.
 7. The drill bit according to claim 1 wherein each planar section extends substantially a full length of the tapered female connecting portion.
 8. The drill bit according to claim 1 wherein the generally cylindrical tapered surface is oriented at a first inclination to a longitudinal axis of the drill bit and the planar sections are oriented at a second inclination to the longitudinal axis of the drill bit which is greater than the first inclination.
 9. The drill bit according to claim 8 wherein a width of each planar section generally in the circumferential direction is reduced from the front end to the rear end of the drill bit.
 10. The drill bit according to claim 8 wherein the first inclination is less than 10 degrees and the second inclination is within 3 degrees of the first inclination.
 11. The drill bit according to claim 10 wherein the second inclination differs by approximately one degree from the first inclination.
 12. The drill bit according to claim 10 wherein the first inclination is approximately 5 degrees and the second inclination is approximately 6 degrees.
 13. The drill bit according to claim 1 in combination with a male connecting portion comprising a generally cylindrical tapered surface adapted to mate with the corresponding tapered surface of the female connecting portion, a planar section formed on the tapered surface in mating alignment with each of the planar sections of the female connecting portion, and an outer end face at a forward end, wherein the socket of the female connection portion comprises an internal end face and the planar sections are oriented relative to the internal end face such that: the internal end face is adapted to be spaced from the outer end face of the male connecting portion when the planar sections of the female connecting portion initially abut the planar sections of the male connecting portion; and the internal end face is adapted to positively engage the outer end face of the male connecting portion when the drill bit is subjected to percussion drilling forces from the drill rod assembly.
 14. The drill bit according to claim 1 in combination with a male connecting portion comprising a generally cylindrical tapered surface adapted to mate with the corresponding tapered surface of the female connecting portion, and a planar section formed on the tapered surface in mating alignment with each of the planar sections of the female connecting portion, wherein the male connecting portion is further integrally connected to a body portion formed at the rear end of the male connecting portion and having a greater diameter than the male connecting portion so as to define an annular shoulder about a rear end of the male connecting portion.
 15. The drill bit according to claim 14 wherein the socket of the female connection portion comprises annular end face at the rear end and the planar sections are oriented relative to the annular end face such that: the annular end face is adapted to be spaced from the annular shoulder of the male connecting portion when the planar sections of the female connecting portion initially abut the planar sections of the male connecting portion; and the annular end face is adapted to positively engage the annular shoulder of the male connecting portion when the drill bit is subjected to percussion drilling forces from the drill rod assembly.
 16. The drill bit according to claim 1 in combination with an adapter having a rear end adapted to be supported on a drill rod of the drill rod assembly, the male connecting portion being defined on a forward end of the adapter, and the body of the adapter being formed of a material having a greater hardness than the drill bit.
 17. The drill bit according to claim 1 wherein the bit face comprises a plurality of protrusions of material having a greater hardness than the body of the drill bit, the protrusions being radially and circumferentially spaced from one another.
 18. A modular drilling system for use with a male connecting portion of a drill rod assembly, the system comprising: a plurality of drill bits, each having a body extending in a longitudinal direction between a bit face at a forward end and a female connecting portion at a rear end; the female connecting portion of each drill bit defining a socket comprising: a generally cylindrical tapered surface adapted to form a mating connection with a corresponding tapered surface of the male connecting portion; and at least three planar sections formed on the tapered surface at evenly spaced apart positions in a circumferential direction about the socket so as to be adapted to provide positive engagement with corresponding planar sections of the male connecting portion; the female connecting portions of the drill bits being substantially identical to one another; and the bit faces of the plurality of auxiliary bits being different in size relative to one another.
 19. The system according to claim 18 in combination with a common male connecting portion comprising: a generally cylindrical tapered surface adapted to mate with the corresponding tapered surface of the female connecting portion of each drill bit; and a planar section formed on the tapered surface in mating alignment with each of the planar sections of the female connecting portion of each drill bit.
 20. A modular drilling system for use with a male connecting portion of a drill rod assembly, the system comprising: an adapter having a rear end comprising a female connecting portion formed with an internal thread so as to be adapted to engage in screw-threaded engagement with a male portion of a threaded drill rod of the drill rod assembly and a forward end defining a common male connecting portion comprising: a generally cylindrical tapered surface; and at least three planar sections formed on the tapered surface at evenly spaced apart positions in a circumferential direction; and a plurality of drill bits, each having a body extending in a longitudinal direction between a bit face at a forward end and a female connecting portion at a rear end, the bit faces of the plurality of auxiliary bits being different in size relative to one another, and the female connecting portion of each drill bit defining a socket comprising: a generally cylindrical tapered surface adapted to form a mating connection with the corresponding tapered surface of the common male connecting portion of the adapter; and a planar section formed on the tapered surface of the female connecting portion in alignment with each of the planar sections of the male connecting portion of the adapter so as to be adapted to provide positive engagement of the planar sections of the drill bit with the corresponding planar sections of the male connecting portion of the adapter. 